Reciprocating compressors are universally employed in heat pump systems for residential building structures and the like and operate in conjunction with outdoor and indoor coils which coils trade functions; the outdoor coil constituting an air source evaporator while under heating mode, for instance. While under cooling mode, the indoor coil becomes the system evaporator and the outdoor coil becomes the air source condenser.
Depending upon the geographical location of the residence employing the heat pump, the loads during summer and winter operation vary. For instance, when in use in the northeastern states, the heat pump system is subjected to high heating loads in comparison to cooling loads, while in the southern states such as Florida, the heat pump system experiences heavy cooling loads during summer operation and light heating loads during the winter months.
Further, to effect low cost construction, normally the compressor units, which may be of the hermetic design, employ single phase electric motors for driving the compressor. Where such compressors are under load during starting, the current loads on the motor are significantly large such that in most cases, the motor must be oversized for starting since the load is higher than normal operation high heating or cooling load conditions, after start up. Further, reciprocating compressors conventionally of the multi-cylinder type have the suction gas simply supplied to all cylinders in parallel under single stage compressor mode with little though to system efficiency both in terms of electrical loads imposed by starting the electric motor under load and loads imposed by refrigeration circuit operation conditions.
Attempts have been made to improve system efficiency by operating the reciprocating multi-cylinder compressor in double stage operation, depending upon system conditions, this being the subject matter of the referred copending application. Further, it has been determined that system efficiency may be improved by incorporating a subcooler between the coils, which functions to subcool the liquid refrigerant downstream of that coil constituting the condenser prior to feeding the liquid refrigerant to the coil acting as the evaporator of the system for expansion within that evaporator coil. In such subcoolers, which also forms a part of the subject matter of the referred to copending application, a portion of the high pressure liquid refrigerant is bled from the system and vaporized in the presence of the total liquid refrigerant in a suitable subcooler heat exchanger to further reduce the temperature of that portion of the refrigerant delivered to the coil functioning as the evaporator under the particular mode, whether it be heating or cooling. The vapor generated in the subcooler, being at a pressure well above that of the vapor pressure from the coil or coils acting as the system evaporator and directed to the suction side of the reciprocating compressor, is permitted to return to the reciprocating compressor crank case for the multiple cylinders to maintain load reversal on the wrist pins of the reciprocating compressor piston and connecting rod assemblies of the multicylinder reciprocating compressor of the referred to copending application.
It is, therefore, a primary object of the present invention to provide an improved, simplified automatic tri-level multiple cylinder reciprocating compressor heat pump system wherein compressor operation is matched to system heating and cooling loads regardless of the unequal load condition with three levels of compressor operation being readily achieved and automatically effected.
It is a further object of the present invention to provide a simplified, automatic tri-level multiple cylinder reciprocating compressor heat pump system, in which, dependent upon indoor and outdoor conditions, the compressor three level operation may be effected by cutting out or adding compressor cylinders to the compressor compression process and/or shifting the compressor drive motor between low and high speed operation.
It is a further object of the present invention to provide an improved tri-level, multiple cylinder reciprocating compressor heat pump system which includes a subcooler for subcooling liquid refrigerant being fed to the heat pump system coil acting as the system evaporator, and wherein the vapor returned from the subcooler is passed over the motor windings in a hermetic reciprocating compressor package open to the compressor crank case and delivered to the low side of a given cylinder.
It is a further object of the present invention to provide an improved air source heat pump three-step tri-level multiple cylinder reciprocating compressor heat pump system which permits thermal energy to be picked up by an outside air coil and supplied selectively to either one or all of an inside air coil, inside hydronic coil, and storage coil, depending upon system needs.
It is a further object of the present invention to provide a simplified tri-level, multiple cylinder, reciprocating compressor heat pump system in which, under mild ambient conditions, thermal energy may be removed from the room being conditioned and stored by way of a storage coil during the day and may be supplied to the same room as usable heat from the storage coil during the night.
It is a further object of the present invention to provide an improved, simplified tri-level multiple cylinder reciprocating compressor heat pump system, wherein heat may be removed from the room being conditioned during high ambient temperature conditions during the day and stored by way of the storage coil within the system for subsequent discharge by way of the outside air coil at night at lower ambient temperature for improved system thermal efficiency.